Non-linear solver

Hi everyone,
I have a question about the solver. In the numerical block there are linear solver and non-linear solver. I’m doubting in which condition should I apply non-linear solver. In my model, only heat transport and groundwater flow processes are included. I’ve seen some examples in ogs5py benchmark but still cannot find a clue when a non-linear solver is applied. Appreciate it if anyone can answer this question.

Selection of solver depends on governing equations of each process and coupling of processes (e.g., H+M, HnM, HT, THM).

For more details, please see

For absolute beginner,I will recommend following books
[1] Koutromanos, I. Fundamentals of Finite Element Analysis: Linear Finite Element Analysis; John Wiley and Sons: India, 2018.
[2] Bear, J.; Bachmat, Y. Introduction to Modeling of Transport Phenomena in Porous Media; Kluwer Academic Publishers: London, 1990; Vol. 4.
[3] Spencer, A. J. M. (1980). Continuum Mechanics. New York, Dover Publications.
[4] Wood, W. L. (1990). Practical time-stepping schemes. Oxford, UK, Oxford University Press.